Two-way wireless messaging systems are becoming increasingly popular. Such systems can provide "guaranteed" message delivery, as well as subscriber unit initiated messages and responses.
To provide reliable inbound messaging from portable subscriber units to the fixed portion of the system, a sufficient number of properly located base receivers are required. Naturally, the cost of the base receivers is easier to justify in areas of high subscriber density than in areas of low subscriber density. For this reason, two-way messaging service providers sometimes elect to provide a mix of two-way and one-way coverage areas in their systems. A service provider may offer, for example, two-way coverage in the metropolitan portions of his system and one-way coverage in the rural portions.
A system having a mix of one-way and two-way portions presents a problem with regard to guaranteed message delivery. Such mixed systems typically simulcast messages throughout the one-way portion, while using either simulcast or directed message delivery in the two-way portion. When a subscriber unit leaves the two-way portion, the controller of the messaging system stops receiving acknowledgments from the subscriber unit in response to messages received by the subscriber unit. The controller can save the non-acknowledged messages for retransmission to the subscriber unit when the subscriber unit again registers with the two-way portion, but the controller must first learn which, if any, of the non-acknowledged messages were actually missed by the subscriber unit. Simply retransmitting all the non-acknowledged messages would be wasteful of airtime and potentially confusing to the subscriber.
Thus, what is needed is a method and apparatus for facilitating a retransmission of missed messages in a wireless messaging system having a two-way portion and a one-way portion. Preferably, the method and apparatus will provide for the retransmission of only the messages which were actually missed, and will operate in a manner that minimizes the inbound communication traffic required between the subscriber unit and the two-way portion of the system for determining the missed messages.